Ben 10:Alien Force premiered a few weeks ago here in Australia and I'm really enjoying it. As a fan of Ben 10 from the beginning, I think it's a natural progression in the story. Unlike say Rugrats All Grown Up, for example, that simply made the characters older for the sake of it.
They wrote ten-year-olds rather accurately (and I would know,I have a brother that age). But now that the characters are my age I can relate to them and they're more interesting. Plus they are all drawn rather attractively. They can do things with the characters that they couldn't do before, such as the relationship between Gwen and Kevin (I especially love Ben's disapproval of it all). Plus they're on their own now, making their own decisions without Grampa Max helping them out.
I miss the old aliens, all of them had such interesting and unique designs. My favorites being Ghostfreak, Heatblast and XLR8 (don't you just love how they sound like they were named by a little boy?). Although I do like Big Chill, the rest of the aliens are unimpressive. But I think this new series is driven much more by plot than by the look of the creatures. Which reflects how Ben probably feels about having an Omnitrix at this stage. He's grown accustomed to it, the novelty of playing superhero has worn off and now he has responsibilities.
I hope this show runs for a long time yet, I hear there's even a live-action movie in the works.